Figure F61. Nb/Y vs. Zr/Y diagram for Kerguelen Plateau basement basalt from Sites 738, 747, 749, 750, 1136, and 1137. The diagonal lines delimit the field of plume-derived Icelandic lavas and mid-ocean ridge basalt (MORB) plots to the right of this field. Fitton et al. (1997, 1998) argued that melts derived by varying extents of melting from a common peridotite source define trajectories nearly parallel to these boundary lines. Average MORB and ocean island basalt (OIB) (Sun and McDonough, 1989), average lower and upper crust (LCC and UCC, respectively) (Rudnick and Fountain, 1995), alkalic basalts from Site 748 (recovered above basement), and the evolved rocks from Site 1137 are shown for reference.